Physical Recycling Breakthrough for PA6: Automotive Component Application Validation

From Figure 1, it can be seen that when the PCR-PA6 content is 0 (composition A), the material's tensile strength is 189 MPa, tensile modulus is 9980 MPa, and elongation at break is 3.3%. As the PCR-PA6 content increases, the overall tensile mechanical properties of the material show a downward trend. When the content does not exceed 20%, the material's properties do not change significantly compared to the new material. When the addition ratio exceeds 30%, the material's tensile mechanical properties decline significantly. For instance, when the PCR-PA6 content is 67.5% (composition F), meaning the entire plastic matrix in the modified plastic is PCR material, the tensile strength is 161 MPa, tensile modulus is 9460 MPa, and elongation at break is 2.8%. Compared to composition A, the tensile strength decreases by 14.81%, tensile modulus decreases by 5.21%, and elongation at break decreases by 15.15%. This is mainly due to the complex degradation, cross-linking, and other aging reactions that occur during the service period under the influence of natural factors such as load, light, heat, water, and oxygen, leading to a decline in the material's overall performance, which becomes more pronounced as the PCR-PA6 content increases.

Relatively speaking, the tensile strength and elongation at break of the material decrease more significantly, while the tensile modulus decreases less.This may be due to the dominant effects of the proportion and orientation of glass fibers in modified plastics, as well as the interfacial bonding strength between the glass fibers and the plastic matrix, on the material's elastic modulus.。

Figure 1 Effect of PCR-PA6 content on the tensile properties of PA6-GF30

From Figure 2, it can be seen that when the content of PCR‐PA6 is 0 (formulation A), the material's flexural strength is 259 MPa and the flexural modulus is 8530 MPa. As the content of PCR‐PA6 increases, the material's flexural strength shows a decreasing trend. Theoretically, the material's flexural modulus should also decrease, but the test data shows a phenomenon of first decreasing and then increasing. When the PCR‐PA6 content is 30% (formulation D), the material's flexural modulus is at its lowest, decreasing by only 1.99% compared to formulation A. This performance deviation may be due to fluctuations during the granulation, injection molding, or testing processes. When the PCR‐PA6 content is 67.5% (formulation F), the material's flexural strength is 221 MPa and the flexural modulus is 8480 MPa. Compared to formulation A, the flexural strength decreases by 14.67% and the flexural modulus decreases by 0.59%.

Figure 2 Effect of PCR-PA6 content on the bending properties of PA6-GF30.

Impact resistance, as a core testing method for evaluating the toughness of plastics, is used to measure the material's resistance to fracture under high-speed impact conditions. It provides an analytical basis for the failure reasons of automobiles under impact load conditions [16]. As shown in Figure 3, when the PCR-PA6 content is 0 (formulation A), the notched impact strength of the simply supported beam is 12 kJ/m², and the low-temperature notched impact strength is 9.4 kJ/m². As the PCR-PA6 content increases, the overall impact performance of the material shows a declining trend. When the PCR-PA6 content does not exceed 20%, the material's performance changes relatively little compared to new materials. For example, in formulation C, the notched impact strength of the simply supported beam and the low-temperature notched impact strength are 12 kJ/m² and 9 kJ/m², respectively. Compared to formulation A, the notched impact strength of the simply supported beam remains unchanged, while the low-temperature notched impact strength decreases by 4.26%. However, when the PCR-PA6 content is 67.5% (formulation F), the notched impact strength of the simply supported beam is 9 kJ/m², and the low-temperature notched impact strength is 6.6 kJ/m². Compared to formulation A, the notched impact strength of the simply supported beam decreases by 25.00%, and the low-temperature notched impact strength decreases by 29.79%, indicating a significant drop.

Figure 3 Impact of PCR-PA6 Content on the Impact Performance of PA6-GF30

From Figure 4, it can be seen that as the PCR-PA6 content increases, the thermal performance of the material changes little. When the PCR-PA6 content is 0 (composition A), the melting point and heat distortion temperature of the material are 221°C and 205°C, respectively. When the PCR-PA6 content is 67.5% (composition F), the melting point and heat distortion temperature of the material are 220°C and 202°C, respectively, with a decrease ratio of 1.46% and 0.45%. It can be seen that the addition of PCR-PA6 has little impact on the melting point and heat distortion temperature of PA6-GF30 modified plastics.

Figure 4 Impact of PCR-PA6 Content on the Thermal Performance of PA6-GF30

Figure 5: Structure of the duct support and finite element model.

The structure contains 4 bolt assembly points, embedded with steel bushings, achieving the connection between the shroud and the cab body through bolt assembly. A 6×6 shell element mesh division is used, and the bolt connection parts adopt a bolt connection method. The model consists of a total of 5.24 million elements. Material properties are assigned to various parts of the model, and loading and constraint settings are carried out according to design requirements for CAE strength simulation analysis. The stress distribution is shown in Figure 6.

Figure 6 CAE Strength Finite Element Analysis Results

According to the simulation analysis results, the maximum stresses on the flow guide bracket under emergency braking, lateral impact, lateral turning, and ESC conditions are 1.9, 3.3, 2.7, and 15.3 MPa, respectively, which meet the design requirements.

Prepare the duct support sample using the above materials and, and conduct low-temperature impact, high-temperature resistance, low-temperature resistance, thermal cycling, chemical resistance, and light aging tests. The test results show that all meet the design requirements, as shown in Table 2.

Table 2 Performance Test Results of Fairing Bracket Parts

Install two fairing bracket samples symmetrically on a certain heavy-duty truck model, with one end fixed to the cab body using two M8 bolts, and the other end fixed to the fairing using two M8 bolts, as shown in Figure 7.

Figure 7 Fairing Bracket Sample Installed

Table 3 Length and Proportion of Each Section

As the content of recycled polycaprolactam (PCR-PA6) increases, the overall performance of 30% glass fiber reinforced polycaprolactam-based composites (PA6-GF30) shows a downward trend. Relatively speaking, the material performance changes are minor when the proportion of PCR-PA6 does not exceed 20%. From the perspective of material performance, the decreases in tensile strength, elongation at break, flexural strength, and impact strength are more pronounced, while the decreases in tensile modulus, flexural modulus, melting point, and heat deformation temperature are less significant.

Select the PA6-GF30 material containing 20% PCR-PA6 to prepare the duct cover support sample. After testing the components and the complete vehicle, it meets the performance requirements. This indicates the feasibility of using modified PCR-PA6 in automotive parts, providing application scenarios and references for the recycling of PA6.